Four-year-olds Holly and Ella Smith and their two-year-old brother Jordan were asleep as the blaze took hold in Freckleton, Lancashire, while elder brother Reece, 19, was overcome by fumes as he went upstairs to try to rescue them.

All four died from the effects of smoke inhalation from the blaze on January 7 last year.

In July, Dyson Allen, 19, was convicted of four counts of manslaughter by a jury at Preston Crown Court who found he had set fire to a bedroom wardrobe.

A birthday party was being held for the children's mother, Michelle Smith, at the address in Lytham Road.

Heavy cannabis user Allen had spent the day drinking vodka and smoking cannabis from a bong.

Sentencing him to life, Mr Justice Males said he had no motive to harm the children or anyone in the Smith family.

He said: "So why did you do it? In one sense, what prompted you to do this terrible thing - not only starting a fire in a room where defenceless young children were asleep but waiting for several minutes before raising the alarm - is a mystery.

"But in another sense, why you did it seems clear enough. It was because you were out of your head due to the lethal combination of alcohol and cannabis which you had taken that day and because of your fascination with fire, particularly when you are affected by drink or drugs."

The judge continued: "If you had not been drinking alcohol and smoking cannabis, four young people would still be alive and several other lives would not have been blighted.

"But although you were intoxicated, you were not so intoxicated that you did not know what you were doing.

"While you did not intend to cause serious harm to the children, you knew what you were doing in starting the fire and you had ample experience of the danger of fire."

He said a life term was required because Allen was someone who poses a significant risk of harm to the public.

Allen - who sobbed throughout the hearing - would only be released when he was no longer deemed a risk, he said.

Allen was cleared of murdering the siblings.

He denied all the charges and claimed it was not him who had started the fire.

The defendant was the only other person who was upstairs at the dormer bungalow when the fire broke out, said the Crown.

The fatal fire took hold from hanging clothes in a wardrobe in the bedroom shared by the three young children and their mother. Three family friends were also in the house with the defendant who was a friend of another of Ms Smith's sons.

Allen was a regular visitor and stayed overnight the evening before the blaze, the jury was told. He spent most of the night on January 7 in the second upstairs bedroom, according to those who were in the house, said prosecutor Neil Flewitt QC.

Ms Smith, 37, said she said remembered the lights going off and then the defendant jumped down the stairs and shouted "Fire'' before he ran through the kitchen and out of the back door.

Ms Smith told police that smoke alarms had been fitted at the top and bottom of the stairs but Reece had taken them down in the days before the fire because one or both of them kept making beeping noises.

Mr Flewitt told the jury that several "'extremely detailed investigations" had taken place into the cause of the fire and the unanimous view of the experts was that it was started deliberately. One expert concluded the fire started in the hanging clothes in the wardrobe, and the most likely source of ignition was a naked flame.

Giving evidence, Allen admitted his involvement in starting a locker fire when he was a pupil at his former high school and also setting fire to a local field.

But he denied claims that he sprayed flaming aerosols at a house party in March 2011.

Mr Justice Males said he had not grown out of a history of playing fires.

He said he was satisfied that under the influence of drugs and drink he did terrorise teenage girls at the 2011 party with his makeshift "flame thrower".

And the week before the deaths he lit an aerosol spray at the house in Lytham Road.